The invention relates to a textile composite material used to stabilize, consolidate or reinforce soils and layers of earth and as a load-carrying filtering layer, e.g. to cover a drainage layer, and comprising a nonwoven.
Nonwovens, especially plastic nonwovens, are used frequently in geotechnical engineeringxe2x80x94for example, in waste impoundment constructionxe2x80x94and in hydraulic engineering to separate two layers of soil having different particle size distributions. Different filtration characteristics can be obtained, depending on the thickness and strength of the nonwoven. Plastic nonwovens made from coarse fibers are suitable for use as drainage layers and are often combined with filtering nonwovens.
The disadvantage of nonwovens, used alone or in textile composites made of various plastic nonwovens, lies in their limited load-carrying capacity. Compared to textiles made of filament yarns (e.g. wovens or knits), nonwovens have much greater stretchability with lower tear resistance. Even textiles such as wovens and knits that possess high tear resistance, which are also used in geotechnical engineering, usually exhibit unfavorable load-carrying behavior, since the application of forces to such textiles initially causes elongation of the material due to the stretching of the yarns, which extend in curved paths as a result of the stitch formation or interweaving. Higher load-carrying capacity develops only after the material has undergone considerable stretching.
DE-A 37 28 255 discloses a ground anchoring strip that includes a loose nonwoven as a drainage material, fastened to the upper side of which, by clamping or sewing, is a textile strip comprising tensile-load-carrying warp strands. The textile strip must be manufactured on a weaving or knitting machine in a separate production step and then brought together with and joined to the nonwoven in a second production step.
The task of the invention is to create a low-cost textile composite material comprising at least one nonwoven fabric and which exhibits high tear resistance in a main load direction and can absorb high tensile forces without undue stretching.
This task is accomplished according to the invention in that exclusively parallel, load-carrying, straight, plastic filament yarns are woven, knitted, sewed or Raschel-knitted onto the nonwoven.
In the use of textile composites in geotechnical and hydraulic engineering, there is nearly always a fly established main load direction, e.g. the direction of inclination of a slope. By the simple expedient of applying exclusively parallel, straight, load-carrying strands made of plastic material, the textile composite material can be rendered highly tear-resistant in one direction, the main load direction. Since the strands lie straight against the nonwoven, when force is applied they are immediately stretched in opposition to their intrinsic elasticity, rather than being initially stretched with much lower resistance, as in the case of wovens and knits.
The plastic filament yarns extending in the warp direction can be applied to the nonwoven inexpensively, on sewing, knitting or Raschel-knitting machines, in a width that corresponds to the width of a web of nonwoven. Suitable plastic filament yarns can be selected according to the field of application and the required load-carrying capacity of the textile composite. One especially low-cost solution is to use split polypropylene yarn as the load-carrying strand and optionally also as the binding yarn for fastening the load carrier to the nonwoven, which can also be made of polypropylene.
The cross section of the strands can range from 2 to 100 mm2, depending on the material of the load-carrying strands and the distance therebetween. The load-carrying strands preferably have a cross section of 4 to 50 mm2 and are separated by a distance of 1 to 100 mm.
In an especially preferred embodiment of the invention, the load-carrying strands are Raschel-knitted onto the nonwoven in respective pairs, the distance between two pairs being 1 to 100 mm. This reduces the amount of binding yarn needed to secure the load-carrying strands. Of course, the connection between the nonwoven and the load-carrying strands is looser in this case than when the load-carrying strands are fastened individually, but such fixing of the load-carrying strands to the nonwoven is adequate. Once installed, both the load-carrying strands and the nonwoven are held in position by the pressure of the superjacent layers of earth.